Fiber optic sensors and self-reference techniques for temperature measurements in different industrial sectors

Mención Internacional en el título de doctorEl objetivo de este trabajo se centra especialmente en el desarrollo de sensores de fibra óptica y técnicas de autoreferencia para la medida de la temperatura en diferentes entornos industriales. El primer objetivo de este trabajo consiste en el diseño y desarrollo de un sensor de fibra óptica de bajo coste para la medida de la temperatura en transformadores de potencia y aplicaciones biomédicas. En estas aplicaciones, el uso de sensores de temperatura tradicionales resulta inadecuado debido a la presencia de fuertes interferencias electromagnéticas que pueden perturbar la lectura de la temperatura. Uno de los requisitos fundamentales para diseñar un sensor de temperatura que pueda usarse en aplicaciones biomédicas es el uso de materiales biocompatibles en su fabricación. En este sentido, una configuración simple que permite cumplir con los requisitos mencionados anteriormente es la modulación por intensidad en fibras poliméricas. Este tipo de sensores basan la lectura de la temperatura en medir las variaciones de potencia óptica en función de los cambios de temperatura que se aplican sobre el sensor. En este contexto, el uso de la tecnología asociada con la fibra óptica de plástico ofrece ventajas competitivas frente a otros materiales, como son: el uso de dispositivos opto-electrónicos de bajo coste, la posibilidad de utilizar conectores de baja precisión, la posibilidad de utilizar multiplexores y demultiplexores de muy bajo coste, entre muchas otras ventajas. A pesar de estas ventajas, los sensores de intensidad necesitan de esquemas de autoreferencia que eviten fluctuaciones de potencia que interfieran en la lectura de la temperatura. Estas fluctuaciones pueden provenir de fluctuaciones de potencia a lo largo del tramo de fibra óptica entre la unidad de control y el sensor, fluctuaciones de la fuente de luz por cambios en la corriente de alimentación, pérdidas de potencia por envejecimiento de la instalación, entre otras causas. El segundo objetivo de este trabajo consiste en promover el estudio y el desarrollo de técnicas de multiplexado y autoreferencia que implementen sensores fabricados en fibra óptica de plástico. Estas topologías deberán de utilizar dispositivos eficientes desde el punto de vista del consumo de potencia para mejorar con ello el balance de potencias del sistema y por tanto, poder utilizar este tipo de esquemas en redes de corto y medio alcance. Para alcanzar este objetivo, en este trabajo se desarrollan técnicas de autoreferencia y multiplexado de bajo coste basadas en multiplexación por longitud de onda vasta (CWDM, Coarse Wavelength Division Multiplexing). Esta técnica se caracteriza por su amplio desarrollo en el campo de telecomunicaciones como estándar para aplicaciones de corto o medio alcance en redes metropolitanas. Los multiplexores y demultiplexores diseñados para esta topología tienen una rejilla de longitudes de onda con una separación entre canales de 20nm. Este espaciado entre canales dificulta la multiplexación de un elevado número de dispositivos o sensores como podría llevarse a cabo si se usaran dispositivos basados en multiplexación por longitud de onda densa (DWDM, Dense Wavelength Division Multiplexing). Pero presentan una clara ventaja competitiva, los esquemas CWDM requieren bajas tolerancias en la fabricación de fuentes de luz, un control menos exhaustivo de la temperatura de la fuente, filtros ópticos de bajo coste y esquemas de diseño menos complejos. Los menores requisitos técnicos de los dispositivos utilizados con esta tecnología hacen que sea una topología interesante para su uso en redes de sensores de bajo coste. El tercer objetivo consiste en desarrollar sensores sin contacto basados en pirometría de dos colores para el sensado de la temperatura en procesos de mecanizado industrial...As a general aim, this work specifically focuses on the development of temperature sensors and self-reference techniques for temperature measurement in different industrial sectors. The first objective of this work is the design and development of a low-cost fiber optic sensor for measuring temperature in power transformers and biomedical applications where the presence of EMI prohibits the use of traditional sensors. Compatibility with the human being is a requirement when the temperature sensors are used in medical applications. Following simple fiber optic configurations, intensity sensors modulate the optical power loss as the temperature changes, thus providing the measurement as an optical intensity modulation signal. Polymer Optical Fiber (POF) technology, with very low-cost components, enables temperature sensing using a low precision connectors and lenses as well as simple multiplexing and demultiplexing devices, especially if compared with glass optical fibers. However, intensity sensors need a self-referencing method to minimize the influences of long-term aging of source and receptor characteristics, as well as undesirable random short-term fluctuations of optical power loss in the fiber link connecting the control unit, where the measurements are taken, to the remote sensing point, where the optical sensor is located. The second objective of this work is to promote, study and develop a multiplexing strategy to implement and scale POF sensor networks using low cost off-the-shelf devices, enhancing the power budget and keeping the self-reference of the measurements. This work focuses on low-cost Coarse WDM (CWDM) technology, where a grid of wavelengths with a 20nm channel spacing for target distance of up to tens of kilometres is specified. CWDM technology have lately been promoted in the field of telecommunication as standard for metro applications with shorter distances, lower network capacity and cost than Dense WDM (DWDM). This topology requires simpler, wider tolerance laser manufacturing, less laser accurate temperature control and reduced design complexity and cost of optical filters. These relaxed requirements make the CWDM technology an interesting approach for building low-cost self-referencing sensors networks. The development of this technology, adapted to the use of POF, can be carried out with the development of fiber Bragg gratings (FBG) in POF, providing an effective and compact strategy for exploiting fiber links for both propagating directions of the light with a single fiber lead. The third objective is to develop a non-contact two-colour fiber-optic pyrometer for temperature measures in the aerospace machining industry, enhancing the location measurement area, reducing the surface emissivity effect and keeping the self-reference of the measurement…The research work of this dissertation has been supported by the following Spanish projects: TEC2009-14718-C03-03 (DEDOS), and TEC2012-37983-C03-02 (CFOOT-TIC) of the Spanish Interministerial Commission of Science and Technology (CICYT); BES-2010-033348, EEBB-I-12-05434 and EEBB-1-13-07511 of the Spanish Ministry of Economy and Competitiveness; PRX12/00007 of Spanish Ministry of Education; P2013/MIT-2790, FACTOTEM-2/2010/00068/001 and S2013/MIT-2790 (SINFOTON-CM) of Autonomous Community of Madrid. Additional financial support was obtained from ICT COST Action TD1001: Novel and Reliable Optical Fiber Sensor Systems for Future Security and Safety Applications (OFSESA) of the European Union.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Tianxin Yang.- Secretario: Ricardo Vergaz Benito.- Vocal: Kevin Heggart

High spatial resolution optical fiber two colour pyrometer with fast response

Among the different temperature measurement techniques providing micrometer resolution none of them provide fast response and easy access to close distances to the target surface in difficult to access areas. Optical fiber pyrometers provide that access but previous works used large optical fibers with numerical apertures limiting the minimum spot size to be measured. In this study, we propose a novel two colour optical fiber pyrometer based on a low diameter and numerical aperture optical fiber, low-noise photodetectors and high-gain transimpedance amplifiers with a high spatial resolution in the micrometre range and fast response. Using standard optical fibers and related devices provides also a low-cost system. The developed pyrometer presents a high spatial resolution of 16 mum for a target surface at 25 mum with a wide temperature range of 300 to 1200°C it being the highest spatial resolution for this kind of temperature systems. Theoretical analysis and measurements for different pyrometer configurations are reported. This study will help further the microthermography applications in machining processes.This work was supported in part by the Spanish Ministry of Science, Innovation and Universities Grant RTI2018-094669-B-C3 and Juan de la Cierva Grant FJCI-2017-31677, in part by the Directorate for Research and Innovation at Madrid region Grants P2018/NMT-4326, Y2018/EMT-4892 and INTECSOLARIS-CMUC3M; and in part by FSE

Optical Fiber Pyrometer Designs for Temperature Measurements Depending on Object Size

The modelling of temperature measurements using optical fiber pyrometers for different hot object sizes with new generalized integration limits is presented. The closed equations for the calculus of the radiated power that is coupled to the optical fiber for two specific scenarios are proposed. Accurate predictions of critical distance for avoiding errors in the optical fiber end location depending on fiber types and object sizes for guiding good designs are reported. A detailed model for estimating errors depending on target size and distance is provided. Two-color fiber pyrometers as a general solution are also discussed

Monitoring temperature on machining processes is enhanced using optical fibers

An IR fiber-optic pyrometer measures temperatures above 250 C close to rotating components where other sensing techniques are unsuitableThis work has been sponsored by the Spanish Ministry of Economy and Competitiveness under grant TEC2012-37983-C03-02.Publicad

Monitoring techniques in broadband access networks

The proceeding at: 17th International Conference on Transparent Optical Networks, ICTON2015, took place at 2015, July 5-9, in Budapest, (Hungary).Broadband access networks needs specific monitoring techniques at the physical layer to provide the quality of service required by the users. Similarities between sensor and access networks will be analysed to get best practices in both scenarios to provide novel monitoring and self-reference techniques.This work has received funding from the Spanish Ministry of Economía y Competitividad under projects TEC2012-37983-C03-02 (CFOOT-TIC) and TEC2009-14718-C03-03, and support from the Comunidad de Madrid project under grant S2013/MIT-2790 (SINFOTON-CM).publicad

Temperature Measurement and Numerical Prediction in Machining Inconel 718

Thermal issues are critical when machining Ni-based superalloy components designed for high temperature applications. The low thermal conductivity and extreme strain hardening of this family of materials results in elevated temperatures around the cutting area. This elevated temperature could lead to machining-induced damage such as phase changes and residual stresses, resulting in reduced service life of the component. Measurement of temperature during machining is crucial in order to control the cutting process, avoiding workpiece damage. On the other hand, the development of predictive tools based on numerical models helps in the definition of machining processes and the obtainment of difficult to measure parameters such as the penetration of the heated layer. However, the validation of numerical models strongly depends on the accurate measurement of physical parameters such as temperature, ensuring the calibration of the model. This paper focuses on the measurement and prediction of temperature during the machining of Ni-based superalloys. The temperature sensor was based on a fiber-optic two-color pyrometer developed for localized temperature measurements in turning of Inconel 718. The sensor is capable of measuring temperature in the range of 250 to 1200 °C. Temperature evolution is recorded in a lathe at different feed rates and cutting speeds. Measurements were used to calibrate a simplified numerical model for prediction of temperature fields during turning.This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER program under grants TEC2015-63826-C3-2-R and DPI2014-56137-C2-2-R, and from Comunidad de Madrid under grant S2013/MIT-2790

Polymer Optical Fiber Temperature Sensor With Dual-Wavelength Compensation of Power Fluctuations

The design and development of a plastic optical fiber macrobend temperature sensor is presented. The sensor can operate in a temperature range from -55 to 70 degrees C and has a linear response versus temperature with a sensitivity of 8.95.10(-4) degrees C-1. The sensor system uses the ratio of transmittance at two wavelengths to implement a self-referencing technique in order to avoid undesirable power fluctuations influence. The transmittance ratio precision is 0.1%. An analysis has been developed to find the two wavelengths which ratio offers the highest linearity and sensitivity response. Experimental results are successfully compared with theoretical approaches.This work was supported by the Spanish Ministry of Economía y Competitividad and Madrid region under Grants TEC2012–37983-C03–02, P2013/MIT-2790.Publicad

Two-Color Pyrometer for Process Temperature Measurement During Machining

A fast fiber-optic two-color pyrometer operating on the optical communication bands is designed for temperature measurements in machining processes. Off-the-shelf low-loss fiber-optic demultiplexers and optoelectronics equipment are used in order to obtain a cost-effective sensing solution while reducing both the temperature measurement error and the minimum measurable temperature. The system is capable of measuring highly localized temperatures without using collimation lens. The designed pyrom-eter allows measuring temperature in the range from 300 to 650 °C, achieving a full-scale temperature error as low as 4%. Factors in-fluencing the temperature measurements are studied in order to identify the sensor limitations, such as a possible damage on the end of the optical fiber, the spectral loss attenuation and responsivity, or the distance between the fiber end and the target. Finally, this pyrometer is applied in a turning process, using a fiber-optic sensor embedded on a standard tool holder. Temperature measurements on the Inconel 718 are reported showing a good agreement with the simulations.This work was supported by the Spanish Ministry of Economía y Competitividad under Grants TEC2012-37983-C03-02, P2013/MIT-2790, and DPI2014-56137-C2-2-R.Publicad

Dual-wavelength speckle-based SI-POF sensor for cost-effective detection of microvibrations

In this work, a novel method for cost-effective remote sensing of microvibrations is presented. The proposed technique detects periodical changes in the spatial distribution of energy on the speckle pattern at the endface of a SI-POF. By employing a dual-wavelength approach it is possible to increase the system sensitivity without changing its maximum mean squared error, which increases the system accuracy as well as its resolution. The system operates in reflective configuration providing a centralized interrogation scheme. The speckle pattern of both wavelengths is demultiplexed at the fiber end before being directly recorded by an off-the-shelf and a cost-effective webcam. The changes in the intensity distribution are processed at the remote interrogation unit. The proposed system is able to detect instantaneous and periodic microvibrations (with amplitudes ranging from 1 to 6 mu m) localized farther than 9 m from the remote interrogation unit.This work was supported in part by the Spanish Ministry of Economy and in part by the European Union Development Fund under grant TEC2015-63826-C3-2-R (MINECO/FEDER), and in part by the Comunidad de Madrid under grant S2013/MIT-2790

Tolerance analysis for efficient MMI devices in silicon photonics

The proceeding at: IX Conference Silicon Photonics, took place at 2014, March, 8 in S. Francisco (USA).Silicon is considered a promising platform for photonic integrated circuits as they can be fabricated in state-of-the-art electronics foundaries with integrated CMOS electronics. While much of the existing work on CMOS photonics has used directional couplers for power splitting, multimode interference (MMI) devices may have relaxed fabrication requirements and smaller footprints, potentially energy efficient designs. They have already been used as 1x2 splitters, 2x1 combiners in Quadrature Phase Shift Keying modulators, and 3-dB couplers among others. In this work, 3-dB, butterfly and cross MMI couplers are realized on bulk CMOS technology. Footprints from around 40um2 to 200 um2 are obtained. MMI tolerances to manufacturing process and bandwidth are analyzed and tested showing the robustness of the MMI devices.This work has been sponsored by the Spanish institutions Ministerio de Economía y Competitividad under project TEC2012-37983-C03-02, and grant EEBB-1-13-07511, Ministerio de Educación under grant PRX12/00007 and Fundación Caja Madrid.Publicad